The simple sugars are among the most important small organic molecules in the cell. The simplest type of sugars, the monosaccharides, are compounds having the general formula (CH.sub.2 O).sub.n, where n is an integer from three through seven. All sugars contain hydroxyl groups and either an aldehyde or a ketone group. Sugar monomers can be combined via a glycosidic bond by the reaction of a hydroxyl group of one sugar with the aldehyde or ketone group of a second sugar to form disaccharides, oligosaccharides and polysaccharides. Because each monosaccharide has several reactive hydroxyl groups, complex sugars can exhibit branching rather than a simple linear architecture.
Simple polysaccharides such as glycogen, which exhibits a repeating structure of glucose monomers, are used principally as energy stores by the cell. Smaller, but more complex oligosaccharides function in other important cellular roles. For example, such oligosaccharides can be linked to proteins or lipids to form glycoproteins or glycolipids, respectively.
In recent years, a major focus for researchers in the area of carbohydrate chemistry has been the glycoproteins. The oligosaccharide side chains of glycoproteins have been implicated in such cellular processes as protection of peptide chains against proteolytic attack, facilitation of the secretion of certain proteins or their mobilization to the cell surface, induction and maintainance of the protein conformation in a biologically-active form, clearance of glycoproteins from plasma, direction of the immune response by acting as immune decays, and function as antigenic determinants in differentiation and development.
Information about glycoprotein sugar side-chain composition, and more importantly their sequence is required to fully understand and establish structure-function relationships. However, glycoproteins are usually available in only limited quantities (typically 1-100 micrograms glycoprotein, containing 1-10% oligosaccharide) making it difficult to determine the sequence and anomeric configuration of glycosidic linkage. Unfortunately, current techniques employed to determine oligosaccharide sequence require milligram quantities of the oligosaccharide species. A need exists for a simplified oligosaccharide sequencing method which is useful to determine the sequence when only small (e.g., microgram quantities) quantities of common oligosaccharides are available.